Nonshrinking yarn



July 27 W43 H. G. INGERsoLL 2325,06@

NON- SHRINKING YARN Filed Feb. 25, 1942 2 Sheezls-Sheel 2 INVENTORHEHIIE. @51151311 ATTORNEY Watented July 27, 1943 NONSHRINKIN G YARNHenry G. Ingersoll, Wilmington, Del., assgnor to E. I. du Pont deNemours & Company, Wilmington, Del., a corporation of DelawareApplication February 25, 1942, Serial No. 432,369

3 Claims. (Cl. 8-11 5.5)

This invention relates to iilaments from normally solid ethylenepolymers and more particularly to the manufacture of filaments of thiskind having improved shrinking characteristics.

Fibers and laments useful in textiles and for other purposes can beobtained by melt extrusion or by other methods from the high molecularweight, normally solid ethylene polymers prepared by polymerizingethylene under pressure. The nlaments thus obtained can be cold drawn,that is permanently elongated under stress in the solid state to yieldproducts oi improved strength, which by X-ray diffraction analysisexhibit molecular orientation along the ber axis. Completely orientedethylene polymer filaments begin to shrink at 45-50 C. This shrinkagegreatly reduces their tensile strength and leaves them in a highlynon-uniform condition. Such shrinkage, for example, warps and distortsfabrics made from such filaments so completely as to materially reducetheir utility. Similar shrinknge eliects are encountered in the case offilaments obtained from other high molecular weight polymers, such asnylon, vinylidene chloride polymers, and from the vinyl chloride-vinylacetate interpolymer known as Vinyon. Various stretch-setting processesdesigned to avoid this difficulty are described in the prior art.Certain of these processes improve to some extent the shrinkageresistance of normally solid ethylene polymer laments, but none producesthe result desired. The previously used method of preshrinking, in whichrelaxed iilaments are shrunk by heat treatment, is ineffective in thecase of ethylene polymer nlaments.

This invention has as an object the manufacture of improved ethylenepolymer filaments. A further object is to provide a method for raisingthe shrinking temperature of these filaments without materially reducingtheir tenacity and other desirable properties. Further objects willappear hereinafter.

The above objects, generally speaking, are accomplished by maintainingthe oriented ethylene polymer filaments at a temperature higher than thedesired initial shrinkage temperature, and below the melting point,while allowing no retraction in the direction of orientation, that is inthe direction of the length of the laments, until there is no furtherreduction in tension, and then heating the filaments in the relaxedcondition at a temperature at least as high as the desired initialshrinkage temperature until substantially no further shrinkage occurs.

The thermal conditioning of ethylene polymer filaments in accordancewith the present process consists of two distinct steps or processes:(1) heat-setting, that is maintaining the laments at constant lengthduring the iirst heating above the desired initial shrinkage temperatureuntil there is no further reduction in tension, and (2) allowingequilibrium shrinkage, that is relaxing under zero tension during thesecond heating. The temperature selected for the conditioning dependsupon the combination of shrinkage and tensile properties desired in thefinished product. Higher temperatures cause a greater reduction iniilament strength but also proportionally raise their initial shrinkagetemperature. Thus, the initial shrinkage temperature of orientedethylene polymer filaments can be raised to a temperature not lower thanabout 40 C. to about 5 C. below the melting point of the polymer bymaintaining the filament in the iirst step at a temperature of from 30C. to 2 C. below the melting point of the polymer. During this firststep the filament is not allowed to retract in the direction of itslength and is thus maintained until there is no further reduction intension. For the second step the filament is heated in a relaxedcondition at a temperature above about 40 C. below the melting point ofthe polymer but not higher than the temperature of the precedingtreatment until substantially no further shrinkage occurs.

To obtain the optimum combination of shrinkage and tensile propertiesthe rst stage of the thermal conditioning is conducted at the maximumtemperature that will not cause lament injury, that is slightly belowthe melting point of the polymer and is continued until there is nofurther reduction in the residual shrinkage of the relaxed lament.Usually this temperature is 2 to 5 C. below the melting point of thepolymer. During the second stage the temperature employed is usually 10to 20 C. below the melting point of the polymer.

The exact time and temperature limits for both stages of theconditioning treatment can be determined by simple test in anyparticular instance. That is, stage (1) of the conditioning is completedwhen the residual shrinkage, that is the tension on the laments heldagainst retraction, is at a minimum, and stage (2) is completed when therelaxed filaments show no more shrinkage. The time and temperaturelimits are interdependent and are influenced also by the grade andorientation of the laments, the heating means used, and the type ofconditioning process, that is whether batch or continuous.

At temperatures of 95 to 103 C. contact times of the order oi one secondsuillce for both stages. In the batch process it is best to useimmersion times of 5 minutes or thereabouts because of the additionalheat capacity of the bobbin and cake.

By residual shrinkage is meant the loss of length upon exposure of therelaxed filament to elevated temperatures.

The requirement of minimum filament tension in the first stage of theprocess corresponds to minimum residual shrinkage. For example, when thechange in tension during heating at constant length is measured by adynamic method wherein the oriented filaments traveling between rollspositively driven at the same speed are heated by a copper block to 100C. and tensions for various heating times at this temperature aredetermined by varying the speed, it is found that the tension increasesrapidly to a maximum, then decreases asymptotically to a constantminimum value after the filaments have been heated for about 0.64second. This asymptotic tension value is the ilnal minimum value, asevidenced by the fact that it is substantially maihtained continuouslywhen the illaments are held at 100 C. for minutes. This value alsocorresponds to the minimum residual shrinkage desired since minimumshrinkage properties are attained when short samples of the laments areheld at constant length at 100 C. for about 1 second.

Various heating means are applicable.' Any type of uid bath may be usedprovided that the fluid does not soften the filaments or injure themmechanically or chemically. For the rst stage in batch processconditioning, it is convenient to hold the laments at constant length ona bobbln. In the second stage it is suspended in the heating medium inskein form. The filaments can be conditioned continuously by runningthem over three consecutive separator rolls. The first two run atexactly the same speed, corresponding to the iirst stage in theconditioning process. The second stage is accomplishedby running thethird roll slowly enough to allow equilibrium relaxation between thelast two rolls. Heated rolls, a heated pin, a hot metal surface or a hotpowder or uid bath placed between the rolls provide satisfactoryheating.

The filaments or bers of yethylene polymer to which this process isapplied can be prepared by extrusion of the polymer in a fluidcondition. Illustrative processes are described in United Statespatents, 2,210,774 and 2,219,700. Before conditioning treatment, thefilaments or bers must be completely oriented, as by drawing to thegreatest extent possible without breakage.

The ethylene polymers useful in the practice lof this invention must becapable of remaining in an oriented condition when allowed to relaxfreely at room temperature and in addition the oriented polymer shouldshow marked shrinkage when relaxed at elevated temperatures. Thesepolymers can be obtained by heating ethylene alone or in admixture withanother polymerizable unsaturated compound under a pressure above 500atmospheres and preferably above 1000 atmospheres and at temperatures offrom 100 to 400 C., and preferably from 150 to 250 C. as described inUnited States patents, 2,153,553, 2,188,465, and 2,200,429, or incontact with water and a per-compound catalyst at temperatures in therange of 40 to 350 C. and at superatmospheric pressures in excess of 3atmospheres. The polymers of ethylene alone are normally solid,correspond in composition substantially to (CH2M, and show a crystallinepattern by X-ray diilraction analysis. The physical properties of thepolymers of ethylene with other polymerizable organic compounds varydepending upon the composition of the polymer and the nature of theorganic compound polymer-ized with the ethylene.

The melting point of the ethylene polymer, as dened herein, is thetemperature of zero tensile strength and can be accurately andconveniently determined by measuring the tensile strength at severaltemperatures near the melting point. The temperature of zero tensilestrength is particularly signiiicant to thermal conditioning since it isclosely associated with the highest permissible setting temperatures.Usually fairly s imilarv results are obtained by other melting pointdeterminations such as by the ball and ring method described in UnitedStates Patent 2,210,771 or by the temperature of sticking to a heatedcopper block.

This invention will `be better understood in connection with theaccompanying drawings in which: Y-

Fig. lis an elevational view of apparatus' that can be used inthe -batchtreatment of the yarn during the irst stage ci the process;

Fig. 2 is asimilar view of apparatus for treating the yam in the secondstage lor the process;

Fig. 31s a diagrammatic view in perspective oi mechanism suitable forcarrying out the invention in a. continuous manner;

llg. 4 is a similar view of a. modied apparatus; an

Figs. 5 to 7 are perspective views of heating means for the yarn whichcan replace that used in Figs. 3 and 4.

In carrying out the invention as a batch process the yarn I, secured atconstant length on the bobbin 2, is immersed in the hot iluid bath 3contained in the vessel 4. The bobbin is then withdrawn from the iluidbath, the yarn cooled, and after being formed into the skein 5 it issuspended in a second hot fluid bath 6 contained in the vessel l. Thebaths 3 and 6 can be heated by any suitable means, for example,electrically or by the ame 8.

In the apparatus shown in Figs. 3 and 4 for continuously conditioningthe yarn, the yarn passes over draw roll-separator roll combinationsreferred to herein as separator rolls composed of the rolls 9, I0 and II with the spaced guide rolls I2, I3 and I4. The rolls 9 and I 0 run atexactly the same speed and the yarn thereby held at; constant lengthwhile heat is applied by means of a hot block I5, the treatment of theyarn between these ilrst two rolls being that of stage 1. The separatorroll II is driven at less speed and runs slowly enough to allowequilibrium relaxation during the heating of the yarn by the hot blockI6 which is the heating at the second stage of the process.

Alternatively, several wraps of the yarn are passed over a heatedseparator roll I1. which completes the rst stage of the process. Theroll I8 then takes up the yarn at a rate which is slow enough to allowthe equilibrium relaxation which is produced at the temperature of theheating block I9.

In Figs. 5 to 7 are shown differentI means for heating the yarn whichcan replace the hot blocks of Figs. 3 and 4. In Fig. 5 the yarn 20passes into a hot fluid bath contained in a vessel 2I provided withgrooved wheels 22, 23 and 24 for guiding the yarn into and out of thebath. In Fig. 6

the numeral 25 indicates a trough containing heated sand 26 throughwhich the yarn passes. In Fig. 7vthe yarn passes a few turns over aheated pin 21.

The examples which follow are illustrative of the practice of thisinvention.

EXAMPLE I Fully oriented fllament yarn having a denier of 90 made froman ethylene polymer having a molecular weight 'of 20,000 and a meltingpoint of 110 C. is wound upon a metal bobbin. Both yarn ends are tiedsecurely and the bcbbin is immersed for 5 minutes in a sodiumchloride-water bath held at 108 C. (stage 1). The bobbin is then cooledand the yarn removed and skeined. The skein is suspended in a 90 C.water bath for 5 minutes and allowed to relax completely (stage 2) Thistreatment remarkably improves the shrinkage characteristics of the yarnWithout substantial decrease in its tenacity, as summarized in Table I.Tenacities here are given in grams per denier based upon the originaldimensions of the yarn (o. d.).

Fully oriented yarn having a denier of 92 and a filament count of 5 madefrom an ethylene polymer having a molecular weight of 9,000 and amelting point of approximately 100 C. is wound upon a metal bobbin. Bothyarn ends are tied to prevent contraction and the bobbin immersed for 5minutes in a water bath held at 95 C. (stage 1). The bobbin is cooledand the yarn rewound in skein form. This skein is then placed in a waterbath held at 90 C. to allow equilibrium relaxation, and removed after 5minutes. This procedure raises the initial shrinkage temperature of theyarn about 52 C. without unduly reduclng the tenacity. The resultsobtained are shown in the following table.

Table II Initial shrinkage shrinks Tenacity Elongage at 90 C. at about(g /d.-o.d.) tion Per cent C. 1 7 Per cez Ori inal 34 40 16 70 1.6 30Stages l and 2 0 92 1.1 57

produces a setting action which in this instance must still necessarilyoccur after the filament has been oriented. It is also possible tocombine both steps of the process into one step procedurally but theactual physical changes must be stepwise. For example, passing severalwraps of nated, laminated, or composite fabrics.

the filament around a heated separator roll would accomplish stage 1 ofthe process. The lament can then be taken over a hot surface for thesecond stage heating and allowed to relax completely before being woundup Crimped bers can be obtained by combining a crimping operation withthe first step of the present process, for example, by using a mandrelof suitable shape. The crimped fibers have a high degree of crimp andare valuable as artiilcial wool since they are highly elastic and areunaffected by moisture. Degree of' crimp refers to the ratio ofstraightened length to crimped length.

The ethylene polymers mentioned herein are intended to include any ofthe polymers which are solid at ordinary temperatures, which contain theethylene constituent in substantial proportions, and which are obtainedby polymerizing ethylene alone or in admixture with at least one other'polymerizable unsaturated organic compound such as other mono-oleilns(propylene or butylene); dichloroethylenes such as 1,2-dichloroethylene,2-chloropropene; tetrafiuoroethylene; vinyl ethers, ketones and ester,and other vinyl compounds such as methyl vinyl ether, methyl and ethylvinyl ketones, vinyl chloroacetate, vinyl propionate, N-vinylphthalimide, vinyl thiolacetate; stilbene; styrene; acrylic andmethacrylic acids, their esters, amides, and imides; esters of maleicand fumarie acids; and esters of itaconic acid.

The ethylene polymers used in the practice of this invention can, ifdesired, be blended with such modifiers as dyes, plasticizers, fillersand the like.

The usefulness of ethylene polymer laments is markedly increased by thepresent process since shrinkage does not occur at temperatures lowerthan 15 or 20 C. below the melting point. Thus, the fibers and filamentsobtained in accordance with this invention are useful for tapered orcylindrical bristles which are used, for example, in rotary brushes forcleaning filter screens, and in brushes for use in plating and picklingbaths. Likewise, the filaments are useful as surgical sutures which canbe readily sterilized by chemical means and are inert to water, and tobody uids and tissues. The laments are also useful as fishing leadersand their property of floating on water makes them of special value asdry-ily leaders. Many types of useful screen which are highly durablecan be fabricated from these filaments. The filaments are also useful inthe fabrication of such articles as fish nets, hair nets, and dentaloss. They can also be used as fibers in currency paper, as corrosionresistant packing, as elastic bers, as wrappings for heat and electricalinsulation, as windings for baseballs and golf balls, and as cords forreenforced rubber articles.

'I'he ethylene polymer laments are also valuable in the manufacture ofyarns, metallized yarns, braided cords, ropes, and coated, impreg- Thefilaments or yarns can be used alone or in admixture with other textilessuch as cotton, silk, rayon, or Wool and the composite materialfabricated into textile fabrics such as by knitting, weaving or felting.

In making felted fabrics or artificial felt, heat is applied to theoriented ber and the resulting shrinkage produces a felting orinterlocking action. An articial leather may be made by felting andfusing the fabric.

Fabrics comprising the ethylene polymer laments of this invention,because of their water resistance, durability, and elasticity, nd manyindustrial applications, for example, in making awnings, tents, sailcloth, Holland cloth, lamp shades, flags, parachutes, gloves, camerabellows, aeroplane fabrics, iilter cloths, corrosion resistant packingsand gaskets, aprons for trade, laboratory and surgical uses, diaphragmsfor gas meters and the like, balloon fabrics, blankets, garters,foundation garments, belting, hosiery, helmets, Suspenders, brassires,jackets, artificial fur, composite fabrics, carpets, rugs, and the like.

As many apparently widely diilerent embodiments of this invention may bemade Without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as dened in the appended claims.

I claim:

1. A process for raising the shrinking temperature of oriented ethylenepolymer filaments selected from the class oi iibers, yarns, and the likewhich comprises maintaining the filaments at a temperature of from 30 C.to 2 C. below the melting point of the polymer while preventingretraction in the direction of the length of the filaments and thenheating the maments in relaxed condition at a temperature above about 40C. below the melting point of the polymer,

vbut not higher than the temperature of the pre- -retraction in thedirection of the length of the iilaments and then heating the laments inrelaxed condition at a temperature at least as high as the temperatureof said rst mentioned shrinking. but not higher than the temperature ofthe preceding treatment.

3. An ethylene polymer lament which does not shrink when heated totemperatures lower than 40 C. to 5 C. below the melting point of thepolymer, and which is obtained by the process dened in claim 2.

HENRY G. INGERSOLL.

